I first saw this on Net-Cool which is a great site to subscribe to for finding really interesting things on the web.
This movie explains some of the reasons of concern for monitoring the increase in temperatures that we have felt since the 1960s. It is very well done and enjoyable to watch. Unlike An Inconvenient Truth, it admits that this is not pure imagery but some CGI has been done.
If you can handle the bandwidth, you will see better graphics here rather than watching the embedded YouTube video below.